This invention relates to an improved inline multiple cylinder engine for motorcycles and more particularly to an improved power plant construction for motorcycles.
One popular type of motorcycle power plant employs a reciprocating engine with a plurality of cylinders that are aligned and which are transversely disposed relative to the longitudinal axis of the motorcycle. It is also the practice with motorcycle power plants to embody a change speed transmission in the crankcase of the engine. In one form of such power plants, the crankcase transmission casing is formed from upper and lower castings that are split along a generally horizontally extending plane and the axis of the engine output shaft and the axes of the transmission shafts lie in this plane and extend transversely of the motorcycle. The cylinder block is then affixed to the uppermost casing. Although this arrangement has a number of advantages, the engine cylinders are generally positioned between the knees of a rider when the engine is disposed in a generally vertically extending position. Such power plant configurations require modification to conventional frames in order to accomodate the width of the engine and this coupled with the engines with itself causes the rider's knees to be positioned at an uncomfortably large angle.
In order to avoid these problems, it has been proposed to incline the cylinder block of the engine at a forward angle. However, with conventional constructions, this has given rise to further problems. If the cylinder block is forwardly inclined, the upper crankcase member tends to become very thin at its forward edge and thus the rigidity of the crankcase can become weakened and other problems result. This can be avoided by increasing the height of the engine but with the forward inclination, this also increases its length and gives rise to further problems is locating and supporting the engine and transmission within the motorcycle.
It is, therefore, a principal object of this invention to provide an improved compact and yet strong power plant for a motorcycle.
It is another object of this invention to provide an improved casing construction for a motorcycle having an inline engine and transversely disposed output and transmission shafts.